Enantioselective Transition-Metal Catalysis via Anion Binding with Chiral Hydrogen-Bond Donors

Asymmetric transition-metal catalysis represents a powerful strategy for accessing enantiomerically enriched molecules. Here, we report a new approach for inducing enantioselectivity in transition-metal-catalyzed reactions that relies on neutral hydrogen-bond donors (HBDs) that bind anions of transition-metal complexes to achieve enantiocontrol and rate enhancement through ion pairing in concert with other noncovalent interactions. A cooperative anion-binding effect of a chiral bis-thiourea HBD is demonstrated to lead to high enantioselectivity (up to 99% enantiomeric excess) in intramolecular ruthenium-catalyzed propargylic substitution reactions. Experimental and computational mechanistic studies reveal the attractive interactions between electron-deficient arene components of the HBD and the metal complex that underlie enantioinduction and the acceleration effect.